Electric current producing cell having depolarizer in intimate contact with carburized surface of the container



Dec. 23, 1969 s. RUBEN 3,485,675

ELECTRIC CURRENT PRODUCING CELL HAVING DEPOLARIZER IN INTIMATE CONTACT WITH CARBURIZED SURFACE OF' THE CONTAINER Filed June e, 1967 ELECTRIC CURRENT PRODUCING CELL HAVING DEPOLARIZER IN INTIMATE CONTACT WITH CARBURIZED SURFACE F THE lCONTAINER Samuel Ruben, 52 Seacord Road, NewI Rochelle, N.Y. 10804 Filed .lune 6, 1967, Ser. No. 649,065 Int. Cl. H01m 11/00 lU.S. Cl. 136-83 11 Claims ABSTRACT 0F THE DISCLOSURE This invention is an electric current producing cell having an alkaline electrolyte, an oxide depolarizer such as manganese dioxide, a metal container of steel or nickel plated steel with which the depolarizer is in intimate contact, the surface of the container with which the depolarizer is in contact having been carburized, so as to provide and maintain a low contact resistance and high lash current.

This invention relates to electric current producing cells and more particularly, a sealed zinc alkaline cell incorporating means for maintaining a low contact resistance between the depolarizer and the contacting container.

When cell depolarizers are consolidated into a steel or nickel-plated steel container and assembled into a primary cell and particularly in cells employing a manganese dioxide depolarizer, contact resistance is developed between the metal surface of the container and the depolarizer. This results in a considerable drop in flash or maximum short circuit current over the life of the cell. In some applications, such as photoash bulb excitation, this increase in contact resistance results in failure or poor timing of the flash. In the past and to overcome this condition, I have used a gold plated surface on the cathode container, as described in my U.S. Letters Patent No. 3,066,179. However, due to the high cost of gold, it is desirable to have a lower cost means of maintaining low contact resistance.

lt is among the objects of this invention to provide a cell with a maximum ash current.

It is also an object of this invention to provide a cell which has a minimum contact resistance between the depolarizer and the steel cathode container.

It is still further among the objects of this invention to provide a cell which will retain the minimum contact resistance between the cathode and the container during use.

It is still further among the objects of this invention to provide a cell which will maintain a low contact resistance on storage.

Other objects will be apparent from the disclosure and from the drawing -which is an elevation partly in section showing a cell according to the present invention.

The invention comprises an electric current producing cell in which the iron or nickel-plated iron container with which the depolarizer is in contact is provided with a carburized surface.

When iron, steel or nickel are exposed at elevated temperatures to hydrocarbon gases, such as acetylene, methane or pyrofax, the surface forms an integral carburized layer which will withstand forming and other mechanical operations. This carbon contact is free of pinholes or other exposed base metal areas and maintains a low contact resistance during shelf life in electric current producing cells.

ln practicing the present invention, there is provided, for example, an alkaline primary cell having an amalgamated zinc anode, a cathode composed of a mixture of 91% MnO2 and 9% micronized graphite, and a steel nited States Patent O ice or nickel plated steel container. A spacer-barrier is placed between the anode and the cathode both to prevent direct contact between the anode and cathode as Well as to absorb and retain substantial quantities of electrolyte. The electrolyte is in the form of a potassium zincated water solution of KOH. A thin, integral carburized layer is provided on the inner wall of the container in contact with the cathode.

A cathode depolarizer is made by mixing 91% of synthetic Mn02 with 9% of micronized graphite and pressing said mixture into cylindrical pellets which are then forced into the steel cathode container having a carburized layer integral with its inner surface.

The spacer-barrier is composed of spirally -wound cellulose with an outer wrapping of parchment. This spacerbarrier is placed inside the cylindrical depolarizer pellets. Cylindrical pellets of amalgamated zinc containing about 10% mercury are placed inside of the central opening in the spacer-barrier. These pellets are formed by pressing the powdered zinc. The pellets rest on a neoprene block or pressure pad which prevents contact with the bottom of the cathode container.

The electrolyte is added by injection into the opening in the center of the anode cylinders and passes into the spacer-barrier which absorbs it. This causes the spacer to swell, filling the space between the anode and the cathode, and thus insuring good electrolytic contact between those elements.

The inner and outer caps are applied with an insulating grommet and the outer can is crimped against the grommet. This seals the cell and presses the anode pellet against the compressible neoprene pad which insures maintenance of good contact with the caps.

The drawing illustrates a cell of the invention composed of an outer can 1, an anode container 3, a cathode in the form of cylindrical pellets 4, and an anode of amalgamated zinc pellets 6. A spacer-barrier 5 is located between the anode and cathode, and absorbent sleeve 7 is placed between outer can 2 and cathode container 3. Plastic grommet 8 insulates can 2 and container 3 from contact with inner cap 9 and outer cap 10. The double cap arrangement prevents leakage and creepage of electrolyte outside the cell.

Beneath the zinc pellets 6 is placed pressure pad 12 which insulates the pellets from contact with the container 3 and also, due to its resiliency, urges the pellets 6 upwards against inner cap 9. This achieves excellent contact between the anode and the terminal caps. On outer cap 10 is anode contact 11 for aiding in obtaining good external contact. The inner can 3, drawn from steel or nickel plated steel, is heated at 1000 to 1200 C. for a period of time dependent upon the depth of reaction desired (usually about 10 minutes) in a hydrocarbon gas atmosphere, such as acetylene, ethylene, methane or other gas capable of decomposing and carburizing the surface of the can, the carburized surface being designated 13. The appearance of the carburized can or container is that of a graphite integral with the metal so that it withstands abrasion in handling and has the electrochemical potential to the depolarizer equivalent to carbon. The carburizing of the surface reduces the contact resistance between the container and the depolarizer and increases the ash current of this cell.

While nickel and iron are the preferred materials to be carburized in respect to lowest cost, titanium containers can be used and carburized by the same process.

In the drawing, drawn cans are shown as the cathode container or cathode contact surface. For some special applications, particularly in the case of rechargeable cells, the container for or other metal member contacting a reversible depolarizer or cathode element may be in the form of a pressed iron or nickel sintered powder 3 which can be carburized by exposure to a hydrocarbon gas at high temperature such as 100() to l200 C. The higher the temperature, the less time it takes to obtain the desired depth of reaction. Temperatures lower than 1000 C. will carburize the metals, but require a much longer time to produce a tough, integral carbon surface.

The teachings of this invention are applicable to similar alkaline cells having other depolarizers, such as HgO. It is also applicable to alkaline cells employing anodes of cadmium.

Iclaim:

1. An electric current producing cell comprising a steel container, a carburized surface integral with the inner surface of said container, the cathode depolarizer consisting preponderantly of a material taken from the class consisting of M1102 and HgO closely tting in said container and in contact with said carburized surface, an electrolyte, an anode and an electrolyte absorbing spacer between said cathode and anode.

2. A cell according to claim 1 wherein said material is M1102.

3. A cell according to claim 1 wherein said material is HgO.

4. A cell according to claim 1 wherein said cathode comprising a hydroxide of one of the metals potassium, sodium and lithium and a carburized surface on said container in contact with the cathode.

7. A cell according to claim 6 in which said compound is M1102.

y8. A cell according to claim 6 in which said compound is HgO.

9. An electric current producing cell comprising a steel container, a carburized surface on the inside surface thereof, a cathode depolarizer in intimate contact with said carburized surface, an anode and an alkaline electrolyte.

10. An electric current producing cell comprising a metal member, a carburized surface on the surface of said member, an oxygen yielding depolarizer consisting preponderantly of a material taken from the class consisting of MnO2 and HgO in intimate contact with said carburized surface, an anode and an electrolyte.

11. A cell according to claim 10 wherein said member is steel.

References Cited UNITED STATES PATENTS 2,481,539 9/1949 Ruben 136-107 3,066,179 ll/l962 Ruben 136-83 3,332,802 7/1967 Clune et al. 136-83 WINSTON A. DOUGLAS, Primary Examiner A. SKAPARS, Assistant Examiner U.S. Cl. X.R. 136-107 

